In commonly owned U.S. Pat. Nos. 6,098,532 and 6,142,068 of Sebastian a continuous press for pressing a thick mat into a thin panel is described that has a press frame, upper and lower press belts having confronting lower and upper stretches defining a press gap extending in a horizontal transport direction, upper and lower flexible intake plates juxtaposed respectively above and below upstream ends of the lower and upper stretches of the upper and lower belts and defining therewith an intake mouth flaring upstream, and a plurality of hydraulic actuators braced between at least one of the intake plates and the frame and operable to deform the one plate and thereby change the spacings of the belts at the mouth. A desired shape of the one plate at the mouth is established in accordance with the thickness of the mat, the density of the mat, and the thickness of the panel. Then an actual shape of the one plate is detected by means of an array of position sensors, the detected actual shape of the one plate is compared to the desired shape, any variation between the actual shape and the desired shape is determined, and the actuators are pressurized to impart the desired shape to the one plate.
Another such press is described in U.S. Pat. No. 5,775,214 of Bielfeldt. It has a heating platen provided on one side of the press and a plurality of press-platen segments arranged on a side opposite to the heating platen. The press-platen segments are resiliently coupled to one another by snap-action hinges and the gap between the press-platen segments and the heating platen is independently adjusted. The workpiece being pressed is pulled through the gap which has been optimally set to produce boards with desired density profiles at a maximum production speed. The problem this patent is aimed at is premature wear of the steel belts caused by making them move around a sharp corner at the intake end of the pressing gap. The various segments of the press platen are set at different spacings to achieve the desired effect.
Finally, U.S. Pat. No. 4,850,846 of Walter describes an apparatus for hot pressing a pressed board mat used in making chipboard panels, fiberboard panels and pressed-board panels that comprises a continuously operating press with a lower press belt and an upper press belt and a conveyor with at least two endless conveyor belts adjoining each other. The press has an intake mouth in which the conveyor extends with a delivery nose directed in the feed direction up to a delivery region in the intake. The delivery nose is movable in the vertical direction, in the transport direction, and in a direction opposite to the transport direction and, because of that, the delivery region is displaceable in the entrance of the press according to the thickness of the pressed board mat to be pressed.
All these systems are relatively complex and do not adequately drive gas out of the mat as it enters the pressing gap. Gas is developed as the mat being press is, in effect, cooked as it passes through the press. Unless gas is driven out, it leads to excessive pressure buildup inside the press in the mat being pressed, as the gas cannot readily escape through the gas-impervious stainless-steel belts. The result is voids in the finished product.